为什么我的数组填充了对象而不是附加它们？

Question

I'm building an app which receives from my server a list of products(for example) and displays them. I am using PHP and Apache to retrieve the list from a SQL Server database(pretty much a REST API). When I am building the array and encoding it, I notice that my array has 10 elements (or more, currently I set this limit for testing) and each one of them is the last one.

I've tried to use $arr[] = $prod or array_push($arr, $prod) , or creating a temporary array and merging them, but still the same result. I also tried switching from a macOS Apache to a Windows install or Linux one (I thought it might be the Apache/PHP version).

$prod = new StdClass(); $arr = array();

$search = $_GET['search'];
$search = "%$search%";

$sql = "SELECT TOP 10
            product, qty
        FROM
            table
        WHERE
            product LIKE ?";
$stmt = sqlsrv_prepare( $conn, $sql, array($search));
sqlsrv_execute( $stmt );
$i = 0;
if ( $stmt === false ) {
    die( print_r( sqlsrv_errors(), true) );
}
else {
    while ( $row=sqlsrv_fetch_array($stmt, SQLSRV_FETCH_ASSOC) ) {
        $prod->mainInfo =  $row['product'];
        $prod->secondInfo = $row['qty'];
        $arr[] = $prod;
    }
}
http_response_code(200);
echo json_encode($arr);

The result is something among these lines(there are more lines, but i only include three since it is irrelevant):

[
  {
    "mainInfo": "product3",
    "secondInfo": "qty3"
  },
  {
    "mainInfo": "product3",
    "secondInfo": "qty3"
  },
  {
    "mainInfo": "product3",
    "secondInfo": "qty3"
  }
]

If there are three products that i am loading. The third product is shown in all of the array's elements. It should be something like this:

[
  {
    "mainInfo": "product1",
    "secondInfo": "qty1"
  },
  {
    "mainInfo": "product2",
    "secondInfo": "qty2"
  },
  {
    "mainInfo": "product3",
    "secondInfo": "qty3"
  }
]

Answer 1

You're modifying the same object over and over again. Even when it was already added to the array, it affects that single object. And your arrays just gets multiple references to the same, single object.

To solve this, make sure that $prod is a new object at each start of the iteration.

So move this line:

$prod = new StdClass(); 

...inside the loop:

while ( $row=sqlsrv_fetch_array($stmt, SQLSRV_FETCH_ASSOC) ) {
    $prod = new StdClass(); // <----
    $prod->mainInfo =  $row['product'];
    $prod->secondInfo = $row['qty'];
    $arr[] = $prod;
}

Alternatively, you can use the (object) cast and assign the new object in one go without the need of a $prod variable:

while ( $row=sqlsrv_fetch_array($stmt, SQLSRV_FETCH_ASSOC) ) {
    $arr[] = (object) [
        "mainInfo" => $row['product'],
        "secondInfo" => $row['qty']
    ];
}

Answer 2

Objects in php are always treated by reference . So, everytime you modify $prod in one place, it is modified everywhere else. To avoid this, clone object and work with cloned copy:

while ( $row=sqlsrv_fetch_array($stmt, SQLSRV_FETCH_ASSOC) ) {
    $newProd = clone $prod;
    $newProd->mainInfo =  $row['product'];
    $newProd->secondInfo = $row['qty'];
    $arr[] = $newProd;
}

Answer 3

Objects update by reference.

What this means is that the values will dynamically change as you modify the object, even you put the object in the array in the past. Basically your modifying the same object over and over.

You can create a new instance of the object with new or clone

while ( $row=sqlsrv_fetch_array($stmt, SQLSRV_FETCH_ASSOC) ) {
    $_prod = clone $prod; //copy the object
    $_prod ->mainInfo =  $row['product'];
    $_prod ->secondInfo = $row['qty'];
    $arr[] = $_prod;
}